Liquid cargoes are typically transported by rail or highway in specially designed rail cars, trucks or trailers which include a containment vessel as a major component thereof. Certain cargoes, such as water or milk are transported with the interior of the vessel at atmospheric pressure while other cargoes, such as LPG's (Liquid Petroleum Gases) are transported with the interior of the vessel under pressure. Usually the transport vessel will be in the shape of an elongated cylinder, carried by a suitable frame and running gear arrangement.
Currently, liquids are allowed to move freely within transport vessels with the result that the vessels cannot be loaded to 100% capacity, due to the physical properties of the products being transported and due to weight or load restrictions placed on transportation vehicles. It is also recognized that expansion due to temperature rises must be accommodated within the vessel. For example, when shipping propane it is necessary to provide 15% of the vessel's volume for fluctuations due to temperature increases, meaning that the vessel can be filled only to a level corresponding to 85% of the vessel's volume. Accordingly, most liquids will move within the vessel as it moves, creating a "sloshing" effect that can produce detrimental results.
Forward, backward and sideways movement of the liquid product during stopping, starting and changing directions can cause accidents, such as vehicle roll-over, and can reduce the driver's ability to stop the vehicle, or change directions, in a smooth predictable manner. It has been reported in the Province of Alberta, for example, that 7 out of 8 roll-overs were largely due to product movement.
In recent years, the diameter of all liquid transportation vessels has been increased in order to accommodate increased permissible gross vehicle weights and upgraded vehicle configurations. For example, the average diameter of propane transportation vessels for road use has gone from 84 inches (213 cm) to 102 inches (259 cm), meaning a raising of the center of gravity of the vessel. This, in combination with the movement of the liquid creates a compound negative effect on the performance of the vessel.
There have been attempts to compensate for product movement, including the provision of transverse baffles or walls. For example, Canadian Patent No. 937,881 of Dec. 4, 1973 illustrates a fuel tank for a vehicle including a telescoping baffle which expands to fill an increasing volume of the tank as the fuel is removed therefrom. While this patent recognizes some benefit to reducing the sloshing effect the invention of the patent would not be practical on the large scale required for transport vessels. Canadian Patent No. 834,687 of Apr. 21, 1970 shows a rail car with a horizontal wall 27,27' therein but there are no anti-sloshing features attributable to the structure disclosed therein.